Reforma a la protección de la producción agrícola

Analysis of skeletal muscle biopsies from M. vastus lateralis of 40 subjects at rest showed back-ground-specific differences on enzymatic, histological, transcriptomic and metabolomic levels. Cit-rate synthase (CS) activity of endurance athletes was about 80% higher in both male and female endurance athletes (ME, FE) compared to sedentary controls (MC, FC). Such a difference in CS activity has been reported before^71,182 and is linked to increased mitochondrial activity in skeletal muscle in response to endurance training. Furthermore, fiber composition was significantly different between groups, with both MC and FC having significantly higher proportions of type IIx fibers, while male and female endurance athletes (ME, FE) had significantly more type I fibers compared to MC and male strength athletes (MS) and FC, respectively. Such differences in fiber types are consistent with pre-vious findings and credited to fiber type conversion from IIx to IIa with physical activity, and targeted hypertrophy of both type I and type IIa fibers in response to endurance or resistance training re-spectively^183–185. Results from RNA sequencing revealed that on the transcriptomic level, the largest numbers of differentially expressed genes (DEGs) were found in the comparisons MEvsMC and FEvsFC with 1097 and 1711 DEGs, respectively. Furthermore, the numbers of DEGs were smaller comparing MEvsFE (135 DEGs) than in MCvsFC (452 DEGs; Fig. 14). The smallest differences existed in MSvsMC (26 DEGs). Results from aero-bic respiration capabilities, as also concluded in several publi-cations95,97,186,187. As a main novel contribution from paper III, re-sults confirm such a shift over a Fig. 14: Number of differentially expressed genes (DEGs; bottom

left) and shared DEGs between comparisons (top right) of male and female control groups (MC, FC) to endurance (ME, FE) and strength trained athletes (MS).

life-long career of endurance training. Furthermore, similar differences between endurance trained and control subjects of the same sex reported in paper III were reported before¹⁸⁷. About 50% of the genes found to be differentially regulated in MEvsMC were also found to be differentially regulated following a 3-month endurance training period in men. And about 30% of the differentially regulated genes in FEvsFC were also found to be differentially regulated following the same 3-month endur-ance training period in women. The previous notion of a shift in genes relevant for aerobic respira-tion is supported by a gene ontology analysis of DEGs in paper III which revealed that the differences between endurance athletes and sedentary controls was mostly associated with cellular respiration and the tricarboxylic acid (TCA) metabolism in both men and women (see paper III Figure 3A,B). The RNAseq-based differences in energy metabolism were phenotypically confirmed by enzymatic assay of citrate synthase which was significantly higher in endurance athletes compared to control sub-jects (paper III, Figure 1C). Regarding sex difference in sedentary controls, DEGs were mostly associ-ated with protein catabolism which was elevassoci-ated in men, however comparing ME and FE, gene on-tology analysis showed higher activity of oxidative mitochondria-related and metabolic pathways (paper III, Figure 3C,D). The same differences were further confirmed by genome-scale metabolic modelling results, revealing amongst others BCAA catabolism, fatty acid oxidation and TCA cycle as largely affected by life-long high-level endurance training resulting in a higher activity in ME and FE compared to MC and FC. A closer investigation of the TCA cycle revealed that key metabolites such as Acetyl-CoA were significantly more abundant and enzymes such as CS were expressed significantly higher in response to life-long endurance training (Fig. 15). Taken together, the discovered differ-ences of endurance trained athletes largely depending on energy metabolism and results from CS

Fig. 15: Genome-Scale metabolic modelling of differences between male endurance athletes and sedentary controls in the TCA cycle. Red colored metabolites, enzymes and pathways are more

activity assays suggest a major adaptation to be an increase in the capacity of the muscle for mito-chondrial metabolic processes. The increased capacity, based on structural adaptations in the mus-cle cell could contribute to the resilience of individuals with extensive endurance exercise back-ground to prolonged periods of detraining and contribute to a concept of muscle memory on a cel-lular rather than on a molecular level, potentially adding another dimension to the concept of “mus-cle memory” mentioned in paper II. While results largely show the difference of endurance athletes to untrained individuals on molecular level, strength athletes seem to be rather close to untrained individuals. However, in a similar way, the resilience of strength athletes to detraining could be based on a cellular memory process - the physical accumulation of muscle mass - rather than solely on molecular principles.

To put these adaptations into a health context, DEGs from the comparisons MEvsMC and FEvsFC were inte-grated with datasets from training intervention stud-ies of males with type 2 diabetes (T2D) compared with subjects with normal glucose tolerance (NGT)¹⁸⁸ and females with metabolic syndrome (MetS)¹⁸⁹ com-pared to healthy subjects. Results show that follow-ing 1 year of trainfollow-ing in T2D men, the number of DEGs regulated in the opposite direction decreased sub-stantially while DEGs regulated in the same direction increased. Similarly, DEGs regulated in opposite di-rection in women with MetS decreased following 6 months of training. Specifically, oppositely regulated genes that reverted in response to a period of train-ing were associated with pathways related to high blood glucose, and insulin resistance. These compar-isons show that on the gene expression level, a pe-riod of exercise training can make metabolically un-healthy individuals more like endurance trained ath-letes which are metabolically healthier. Such a trans-formative process with exercise training over a 6- to 12-month period may also be viewed as a form of

memory of (non-)exercise and diseases such as T2D and metabolic syndrome. Such diseases can result in self-reinforcing metabolic and systemic mechanisms. For example T2D can result in muscle loss¹⁹⁰, which in turn would reduce the size of the metabolic buffer that is skeletal muscle. Chronic hyperglycemia can negatively regulate aerobic adaptation, in turn inhibiting exercise-related meta-bolic improvements that could help manage hyperglycemia¹⁹¹. A self-reinforcing mechanism would as a result delay a reversion by exercise and create a “dragging” memory effect that can, in its basic principle be seen as in way similar to a memory effect to training, however in an antithetical sense.

Fig. 16: Comparison of DEGs in ME vs MC and persons with type 2 diabetes (T2D) vs per-sons with normal glucose tolerance (NGT) before and after a year of training (A) and FE vs FC and individuals with metabolic syn-drome (MetS) vs healthy subjects (B) after 6 months of training.